Optimum aerodynamic bicycle wheel

ABSTRACT

Embodiments described herein improve airflow around bicycle wheels by providing for one or more of: (1) a optimum leading edge width of a rim for preventing early stall in cross winds, while still allowing for sufficient stability without undue drag, whilst not unnecessarily increasing the rotating wheel and drag on the frame; (2) a sidewall shape with a subtle camber angle at the leading, which defines a rate of radius change at the max width of the rim—which further defines the max width and placement along the chord length for optimizing the aerodynamic properties of the rim; (3) a continuous rate of change of curvature at a spoke face, which fundamentally improves the performance and stability by generating a side force at higher yaw angles; and (4) wheel sets with a wider front rim relative to a narrower rear wheel to assist in flow attachment in high crosswind areas.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.13/633,629, filed Oct. 2, 2012, which is a continuation of InternationalPatent Application No. PCT/GB2011/001648, filed Nov. 25, 2011, whichclaims the benefit of U.S. Provisional Patent Application No. 61/417,278filed Nov. 25, 2010, all of which are hereby incorporated by reference.

BACKGROUND

Most everyone experiences the joy of riding a bicycle at one point intheir lifetime, and many learn to ride at a very young age. Because ayoung child can master its basic principles, the act of riding a bicycleitself appears very simple. The physics behind the exhilarating ride,however, are anything but simplistic. The cyclist needs to overcomenumerous types of forces acting on the properties of balancing,steering, braking, accelerating, suspension activation, vibration, andmany other bicycling characteristics. Moreover, many of the forces ineach physical realm are open to change and depend on their surroundingenvironment and/or forces from other properties, which adds severalorders of complexity.

To consider the complexities of a bicycle as a whole becomes somewhatoverwhelming. Separately evaluating each force, however, that acts onthe various properties of a bicycle ride makes the task somewhatmanageable. For example, if we consider a cyclist or rider and herbicycle as a single system, two groups of forces emerge that act on thatsystem and its components: internal and external forces. Internal forcesare mostly caused by the rider and the rider's interaction with thebicycle (e.g., by bicycle component friction). External forces, on theother hand, are due to gravity, inertia, contact with the ground, andcontact with the atmosphere.

While the internal forces can have a significant impact on bicycleperformance, most any bicycle racer will agree that the largestresistance comes from the induced external force of the bicycle'smovement through the air. As a rider attempts to move faster, theatmospheric drag and crosswind forces become greater, which in turnrequires the rider to expend greater energy to overcome them. Thus,these forces become an important consideration in bicycle designs,especially in the areas of bicycle racing and triathlons.

Traditionally, bicycle structures such as frames, seat tubes, forkblades, shift levers, etc. have generally circular or otherwisegenerally uniform smooth curvilinear cross-sectional shapes. Suchstructures have cross sections with relatively low length-to-widthaspect ratios. As used herein, the aspect ratio of a cross section isdefined as the unit length over the unit width wherein the length isoriented to be generally aligned with a direction of travel of thebicycle structure. For example, a bicycle structure having a crosssection with a circular shape has an aspect ratio of approximately 1.During cycling, bicycle structures having aspect ratios of approximately1 experience airflow detachment about a portion of the perimeter of thecross section of the bicycle structure. The airflow detachment creates aswirling and often turbulent region of airflow in a wake regiongenerally immediately behind the respective bicycle tube. The wake inthe airflow is indicative of energy dissipation and relatively highlevels of drag associated with the bicycle structures, and thus, thebicycle.

In an effort to reduce the external drag forces associated with airflowoperation of the bicycle, manufactures now design and construct bicyclestructures with improved aerodynamic characteristics. One such widelyaccepted solution has been to provide the bicycle structure in anairfoil shape, which are most often associated with airplane wings,automobile spoilers, marine parts (commonly referred to as hydrofoils orhydrofins), and other aerodynamic systems.

Regardless of the specific application of the airfoil-shaped structure,the cross sections of airfoils generally have lengths that are severaltimes greater than their widths. A forward facing portion of theairfoil, or the leading edge, is generally curved, although other shapesare possible, and configured to be oriented in a forward facingdirection relative to an intended direction of travel. Generally,oppositely facing sidewalls extend rearward from the leading edge andconverge at a trailing edge of the cross section of the airfoil.

The trailing edge forms the termination of the airfoil and is typicallyadjacent a narrowed, pointed tail section of the airfoil. A chord thatextends between the leading edge and trailing edge of the cross sectionis indicative of the airfoil length and is generally many times longerthan the longest chord extending between the oppositely facing sidewallsof the cross section. Chords that extend between the widest sections ofadjacent sidewalls of the airfoil are indicative of the width of theairfoil. Providing an airfoil having a length that is greater than thewidth yields an airfoil having a cross section with an aspect ratio thatis generally many times larger than a value of 1.

The higher aspect ratio allows the airflow directed over the airfoil toconform to the shape of the airfoil and reduces the potential that theairflow will detach from the walls of the bicycle structures (ascompared to bicycle structures that have lower aspect ratios or ratiosnearer to 1). Similarly, the increased aspect ratio reduces the size ofthe turbulent wake region that generally forms immediately behind thebicycle structure; thus, reducing the overall external drags of thebicycle or system. Although such airfoil shapes provide reduced dragperformance as compared to structures having lower aspect ratios, suchshapes are not without their respective drawbacks or limitations.

For example, international bicycle racing regulations limit thepermissible cross sections for bicycle frame tubes. These regulationsdefine a maximum length and a minimum width of the shape of the crosssection and thereby effectively define a maximum allowable aspect ratio.For many experienced riders, this maximum allowable aspect ratio is farless than ideal for reducing the amount of drag experienced by a rider.That is, many experienced rider's prefer bicycles with enhanced aspectratios beyond the regulated limits; however, if they wish to engage inmany racing events, they must adhere to the imposed limitations. Thus,while airfoil-shaped bicycle structures experience lower levels of dragas compared to traditional blunt cross sections, e.g., circular, theregulated airfoil-shaped tubes cannot realize the aerodynamicimprovements possible with airfoils having higher aspect ratios.

In addition to the regulated performance considerations above, practicalconsiderations also limit the attainable aspect ratios of bicyclestructures. For example, as the length of the cross section increasesand the width of the cross section decreases with increased aspectratios, the strength and/or lateral stiffness of the bicycle structuredecreases. In other words, the elongated shape of the cross section thatimproves airflow also detracts from the lateral strength of the bicyclestructure. Although attempts to resolve this relationship yielded frameassemblies with improved lateral strength performance, they ofteninherit increased weight that nearly offset the benefits achieved withthe improved aerodynamic performance. Accordingly, there exists a finebalance between the structural integrity and the weight of the bicycleframe when altering the shape of the cross section to achieve a desiredaspect ratio.

Another shortcoming of many known airfoil constructions is thedifficulty associated with forming the tapered tail section of theairfoil shape. The tail of a common airfoil-shaped structure isrelatively narrow and gradually transitions to the generally pointedtrailing edge of the airfoil. Forming a blemish free pointed tailsection is fairly difficult to manufacture and can be particularlyproblematic in the composite molding processes that are commonlyutilized for manufacturing bicycle structures such as frames, frametubes, fork tubes, and the like. Simply, it is difficult to maintain thedesired shape of the frame tube sections with the materials andprocesses common to current bicycle frame construction.

Accordingly, there exists a need for a bicycle structures with improvedaerodynamic performance that do not overly detract from the lateralstrength of the system and preferably comply with international bicycleracing regulations.

BRIEF SUMMARY

Example embodiments of the present invention overcome theabove-identified deficiencies and drawbacks of current bicyclestructures. For example, embodiments described herein optimize theairfoil shapes of bicycle components (most notably in the bicyclewheels), which provide for overall enhanced performance yet remainrigid, durable, and in compliance with international racing standards.More specifically, example embodiments improve airflow around thebicycle wheels by providing for one or more of: (1) an optimum leadingedge width of a rim for preventing early stall in cross winds, whilestill allowing for sufficient stability without undue drag; (2) asidewall shape with a subtle camber angle at the leading edge, whichdefines a rate of radius change at the maximum width of the rim; (3)based on the optimum leading edge and subtle camber angle, anotherembodiment further defines the max width and placement along the cordlength for optimizing the aerodynamic properties of the rim; (4) acontinuous, evenly distributed, uniform, and/or gradual rate of changeof curvature at a spoke face, which fundamentally improves theperformance and stability by generating a side force at higher yawangles; (5) a virtual double leading edge airfoil rim, which combinesthe tire as a leading edge of the rim with a large spoke hole faceradius at a trailing edge, thereby providing optimum airflow in bothdirections; (6) a rim that both minimizes the rate of change ofcurvature and maximizes the spoke hole radius to a level which producesa balanced side force of airflow in each flow direction, thus virtuallyeliminating cross wind effects; (7) an overall combined geometric shapeof a rim that produces optimal airflow and attachment, through thecombining of the aforementioned features into a single rim; and (8)wheel sets with differing front rims relative to a rear rim forassisting in overall flow attachment and minimal drag around and on thebicycle and in high crosswind areas. Note that this Summary simplyintroduces a selection of concepts in a simplified form that are furtherdescribed below in the Detailed Description. Accordingly, this Summarydoes not necessarily identify key features or essential aspects of theclaimed subject matter and is not intended to be used as an aid indetermining the scope of the claimed subject matter.

Additional features and advantages of the invention will be set forth inthe description which follows, and in part will be obvious from thedescription or may be learned by the practice of the invention. Thefeatures and advantages of the invention may be realized and obtained bymeans of the instruments and combinations particularly pointed out inthe appended claims. These and other features of the present inventionwill become more fully apparent from the following description andappended claims or may be learned by the practice of the invention asset forth hereinafter.

BRIEF DESCRIPTION OF THE DRAWINGS

In order to describe the manner in which the above-recited and otheradvantageous features of the invention can be obtained, a moreparticular description of the invention briefly described above will berendered by reference to specific embodiments thereof which areillustrated in the appended drawings. Understanding that these drawingsdepict only typical embodiments of the invention and are not thereforeto be considered to be limiting of its scope, the invention will bedescribed and explained with additional specificity and detail throughthe use of the accompanying drawings in which:

FIG. 1 is an overall view of a typical bicycle with associatedcomponents and structures that can benefit from one or more improvementsof the present invention;

FIG. 2 is a side view of a wheel that may employ various embodiments ofthe present invention;

FIG. 3 is a perspective view of the wheel in FIG. 2;

FIG. 4 is a cross section of the wheel depicted in FIGS. 2 and 3 in theplane defined by lines 5-5 in FIG. 3, which shows a cross-sectional viewof a tubular type rim and also defines a camber angle that may employvarious embodiments of the present invention;

FIG. 5 is a transverse cross section as formed by lines 5-5 in FIGS. 2and 3, showing an alternate clincher rim that can also utilize variousembodiments of the present invention;

FIGS. 6A and 6C illustrate a cross-sectional view of a typical shapedrim and its corresponding unidirectional airfoil shape with the standarddimensions;

FIGS. 6B and 6D illustrate a cross-sectional view of a virtual dualleading edge shaped rim and its corresponding bi-directional airfoilshape or airflow pattern in accordance with exemplary embodiments;

FIG. 7 illustrates the discontinuity for a rate of change of curvaturearound a cross section of a typical prior art rim;

FIG. 8 illustrates how to define the radius and rate of change ofcurvature for describing exemplary embodiments of the present invention;

FIG. 9 shows measured yaw angles compared to aerodynamic drag forstandard rims and optimum rims that utilize various advantageousfeatures of the present invention;

FIGS. 10A and 10B illustrate many optimum features of a cross sectionfor a 70 millimeter (mm) depth rim and the continuous rate of change ofcurvature achieved from such optimization in accordance with exemplaryembodiments described herein;

FIG. 11 illustrates a continuous rate of change of curvature having G3continuity for various standard sized wheel depths in accordance withexemplary embodiments of the present invention;

FIGS. 12A, 12B, and 12C illustrate the leading edge width and placementof maximum width as a percentage of the rim depth along the cord inaccordance with exemplary embodiments of the present invention;

FIG. 13 is a cross-sectional view of a 35 millimeter depth rim describedin Table 3;

FIG. 14 is a cross-sectional view of a 45 millimeter depth rim describedin Table 3;

FIG. 15 is a cross-sectional view of a 60 millimeter depth rim describedin Table 3;

FIG. 16 is a cross-sectional view of a 70 millimeter depth rim describedin Table 3;

FIG. 17 is a cross-sectional view of an 85 millimeter depth rimdescribed in Table 3;

FIG. 18 is a cross-sectional view of a 95 millimeter depth rim describedin Table 3; and

FIG. 19 is a cross-sectional view of a rim illustrating the variouspoints at which the radius of curvature were measured for the datacontained in Tables 3 through 9.

DETAILED DESCRIPTION

The present invention extends to methods, systems, and devices foroptimal drag reduction of bicycle wheels caused by crosswind and otherexternal factors. For example, one embodiment limits the leading edgewidth of the rim for optimal aerodynamics around the bicycle, whilsthaving sufficient width to limit stall. Similarly, other embodimentsreduce the overall drag of bicycle wheels by optimizing the sidewallshape with a subtle camber angle for preventing sidewall detachment andturbulence and maintain optimum airflow over a wide series of yawangles. Still other embodiments provide for a spoke face for a rim witha continuous, evenly distributed, uniform, and/or gradual rate of changeof curvature (i.e., no sudden steps or changes in surface area anglesespecially around or near the trailing edge of the rim) for improvingoverall stability and performance by generating a side force at higheryaw angles (i.e., when the flow is in the opposite direction on the backof the rim or wheel). Another embodiment provides for a virtual doubleleading edge airfoil rim for optimizing airflow in all directions bycombining the tire as a leading edge of the wheel with a large spokehole face radius at the trailing edge—which becomes the leading edgefrom the backflow side of the rim or wheel. Thus, the wheel or rimbecomes balanced because the side forces on the front and rear of therim or wheel are tuned to balance each other to reduce or eliminate anyturning moment generation. Still yet, another embodiment improves theoverall aerodynamics of the bicycle system by defining wheel sets withdiffering front and rear wheels shapes and sizes for assisting inoverall flow attachment and minimal drag around and on the bicycle andin high cross wind areas.

Prior to describing the above advantageous features of the presentinvention in detail, the following few sections generally describe termdefinitions for use in understanding various embodiments of the presentinvention. In addition, some of the following diagrams describe ingeneral various aspects, properties, or features of current bicyclestructures and systems that may utilize many of the advantageousrealized by the present invention, as described in detail subsequentthereto.

DEFINITIONS

Airfoil: the two dimensional cross section of a bicycle tube, whichtypically represents a streamlined aerodynamic shape defined in thewaterline plane.

Aspect Ratio: The ratio of the major chord (length or total rim depth)to the minor chord (max width) of a two-dimensional airfoil.

Boundary Layer: the layer of slower-moving fluid immediately next to theairfoil wall.

CFD: Computational Fluid Dynamics or computer software that simulatesfluid flows and can be used to predict aerodynamics.

Camber Angle (Sidewall): as used herein refers to the angle between thesidewall of a rim and a hypothetical perpendicular line adjacentthereto.

End-effects: the flow across the end of a finite-length airfoil sectionwhich generally increases drag and reduces lift.

Leading Edge (LE) of a Rim: is one of two edges of the rim that holdsthe sidewall of the tire and forms part of the wheel bed securing thetire to the rim. Such edge may take the form of a flange in the case oftraditional “clincher” type wheels or may take the shape of a shallowlip that forms a cusp where the tire lies for tubular or sew-up rims.Note that this can also refer to the distance between the tire bed andthe tip of the leading edge (measured in mm) depending on the usethereof.

Leading Edge Width: is the inner width between the two leading edges atthe very tip thereof or the furthest point forward on the tire bead oredge.

LE Sidewall: is related to the leading edge and defines where thesidewall begins relative to the leading edge. While the sidewallgenerally has a large gradual curvature, the rim within a few mm at theleading edge has a radius that is much smaller.

LE Sidewall Width: defines the width of the rim at the LE Sidewall,which is generally at the wheel bed where the tire or tube sits withinthe rim sidewalls.

Max Width: refers to the maximum width of the rim, which typicallyexceeds the LE Sidewall width and occurs some distance along the chordof the rim measured from the leading edge (i.e., considering the totalrim depth), which can further be defined by a camber angle describedabove and hereinafter.

Pitch: the vertical angle of tilt of a component, e.g., a down tube hasa nearly 45 degree pitch.

Rate of Change of Curvature or Gradient: defines the difference incurvature or radius change over a given surface per curvilinearmillimeter (mm). In particular, a radius of curvature, R, of a curve ata point is a measure of the radius of the circular arc which bestapproximates the curve at that point. It should be recognized that atany intersection point along a curve of a two-dimensional cross-section,a line can be drawn that is tangent to the curve. The radius ofcurvature (R) at the point is then measured perpendicular to thetangency line. From the radius of curvature (R), the curvature (K) canbe expressed using Equation 1 below, which in its simplest form it canbe considered as the inverse of the radius of a circle.

$\begin{matrix}{K = \frac{1}{R}} & {{Equation}\mspace{14mu} 1}\end{matrix}$

where:

-   -   K=Curvature    -   R=Radius of Curvature

The rate of change of curvature (or gradient) simply is a ratio of thechange in curvature between two measurement points (P₁, P₂) and thecurvilinear or travelling distance (L) between the two points (P₁, P₂).The rate of change of curvature or gradient (∂K) can be represented byequation 2 below.

$\begin{matrix}{{\partial K} = \frac{\left( {K_{2} - K_{1}} \right)}{L}} & {{Equation}\mspace{14mu} 2}\end{matrix}$

where:

-   -   ∂K=Rate of change of curvature or gradient    -   K₁=Curvature at measurement point P₁    -   K₂=Curvature at measurement point P₂    -   L=Curvilinear or travelling distance between points P₁ and P₂.

Rim: generally, the outer portion of a wheel assembly that holds thetire (which represents the leading edge of an airfoil shape of the rim)on the outer surface and spokes through spoke holes of an inner surface(which then becomes the trailing edge of the airfoil shape). Note thatembodiments described herein may refer to either the wheel or rim, andthus the terms become interchangeable herein; however, when used in aclaim the term “rim” does not include the tire, spokes, and or hubassembly unless otherwise claimed.

Spoke Face: the surface of the rim where a spoke of a wheel extends forattachment to the hub. Note that if referred to as a distance, itrepresents the radial distance extending from the chord of the rimtoward the LE Sidewall to a point where the rate of change of curvaturedramatically increases—which generally starts on one sidewall at about ⅔the total rim depth measured from the LE and continues to the same pointon the opposite sidewall.

Traditional Airfoil: a teardrop-like shape with a pointed or generallytapered tail.

Toroid or toroidal: means a surface generated by a plane closed curverotated about a line that lies in the same plane as the curve but doesnot intersect it and generally represents the airfoil shape of manybicycle component designs in accordance with exemplary embodiments.

Waterline: a plane parallel with the ground which slices through abicycle tube (much like surface of water if the tube were partiallysubmerged) and represents the direction of air travel; thus, determiningthe effective airfoil that the air sees.

Wheel: generally herein, a wheel includes the outer circular rim thatholds the tire along with the spoke and hub assembly; however, based onthe embodiment described, a wheel and rim may be used hereininterchangeably.

Yaw: the angle between the total airspeed vector and the direction ofbicycle motion.

General Description of Bicycle Components

FIG. 1 shows a bicycle 1 having a number of bicycle structures 11constructed according to example embodiments of the present invention.As described further below, it is envisioned that bicycle structures 11can include a bicycle frame, tube, a fork blade, a wheel, a tire, ahandlebar, a handlebar stem, a seat post, a pedal crank arm, a dropout ashift lever, a cable guide, a cable, a bicycle accessory such as a waterbottle, and/or a bicycle accessory holder constructed according toexemplary embodiments of the present invention.

Bicycle 10 includes a frame 12 that supports a rider and forward andrearward wheel assemblies. Bicycle 10 includes a seat 14 and handlebars16 that are attached to frame 12. A seat post 18 is connected to seat 14and slidably engages a seat tube 20 of frame 12. A top tube 22 and adown tube 24 extend forwardly from seat tube 20 to a head tube 26 offrame 12. Handlebars 16 are connected to a stem 28 that passes throughhead tube 26 and engages a fork crown 30. A pair of forks 32 extend fromgenerally opposite ends of fork crown 30 and are constructed to supporta front wheel assembly 34 at an end or fork tip 36 of each fork 32. Forktips 36 engage generally opposite sides of an axle 38 that isconstructed to engage a hub 40 of front wheel assembly 34. A number ofspokes 42 extend from hub 40 to a rim 44 of front wheel assembly 34. Atire 46 is engaged with rim 44 such that rotation of tire 46, relativeto forks 32, rotates rim 44 and hub 40.

Bicycle 10 includes a front brake assembly 48 having an actuator 50attached to handlebars 16 and a pair of brake pads 52 positioned ongenerally opposite sides of front wheel assembly 34. Brake pads 52 areconstructed to engage a brake wall 54 of rim 44 thereby providing astopping or slowing force to front wheel assembly 34. Alternatively, adisc brake assembly including a rotor and caliper may be positionedproximate hub 40 of front wheel assembly 34. Such assemblies are readilyunderstood in the art. Understandably, one or both of front wheelassembly 34 and a rear wheel assembly 56 of bicycle 10 could be equippedwith rim-based or disc-based braking systems.

Similar to front wheel assembly 34, rear wheel assembly 56 is positionedgenerally concentrically about a rear axle 58 such that rear wheelassembly 56 rotates about rear axle 58. A seat stay 60 and a chain stay62 offset rear axle 58 from a crankset 64. Crankset 64 includes a pedal66 that is operably connected to a chain 68 via a chain ring or sprocket70. Rotation of chain 68 communicates a drive force to a rear section 72of bicycle 10 having a gear cluster 74 positioned thereat. Gear cluster74 is generally concentrically orientated with respect to rear axle 58and includes a number of variable diameter gears. Understandably,sprocket 70 could also be provided with a number of variable diametergears thereby enhancing the gearing ratios that can be attained withbicycle 10.

Gear cluster 74 is operationally connected to a hub 76 of rear wheelassembly 56. Rear wheel assembly 56 includes hub 76, a number of spokes78, and a rim 80. Each of the number of spokes 78 extend between hub 76and rim 80 and communicate the loading forces in-between. As is commonlyunderstood, rider operation of pedals 66 drives chain 68 thereby drivingrear wheel assembly 56 which in turn propels bicycle 10. Front wheelassembly 34 and rear wheel assembly 56 are constructed such that spokes42, 78 communicate the forces associated with the loading and operationof bicycle 10 between hubs 40, 76 and rims 44, 80, respectively. It isappreciated that bicycle 10 could form a mountain or off road bicycle ora road bicycle, or a bicycle configured for operation on paved terrain.Although more applicable to bicycles that commonly attain greateroperating speeds, it is envisioned that a variety of bicycleconfigurations may benefit equally from the present invention.

As explained in greater detail below, example embodiments provide for abi-directional airfoil rim. In order to understand such embodiment, FIG.1 illustrates a waterline cross-sections of wheel 34 represented byintersecting lines 3-3 and 4-4. Provided the direction of travel asshown, a rim 44 has a front or forward facing section represented by thewaterline cross-section 3-3, and a backward or reverse airflow sectionalong the waterline cross-section 4-4. As such, tire 46 acts as aleading edge for a first airfoil, while a spoke face for rim 44represents the trailing edge, in the forward direction of travel. Whenrotated 180°, the spoke face for the rim 44 now becomes a leading edgeand the tire acts as the trailing edge of airflow around the back of thewheel 34 or reverse airflow direction.

Note that conventional rims only consider the airfoil shape in theforward direction or at the front of the rim. As such, the design of aaerodynamic rim 44 typically resembles a airplane wing shape whencombined with the tire, i.e., with a larger radius leading edge of thetire 46 and a thin tapered trailing edge represented by a narrow radiusor pointed spoke face (usually limited by the spoke 42 diameter and its42 securing mechanism to the rim 44). In other words, up until thepresent invention, conventional wisdom designed rims 44 for aerodynamicefficiency by creating as near of teardrop shape as possible,constrained only by the limitations of the spokes 42. Such design,however, only considered the forward direction of airflow around the rimand ignored the reverse direction or backside of the wheel.

As described in greater detail below, example embodiments of the presentinvention expel the notion of conventional airfoil shapes by creating abi-direction airfoil with virtually dual optimum leading edges. Morespecifically, example embodiments provide for a first leading edge of anairfoil as before, i.e., represented by a tire 46 attached to the rim44. Unlike traditional spoke face designs, however, embodimentsdescribed herein provide for a large radius spoke face with a gradual,uniform change in radius extending from the sidewalls of the rim to thecenter for the spoke hole face. Such large radius spoke face in thereverse direction forms a second leading edge in the rearward directionof airflow on the rim; thus forming a optimum bi-directional airfoil rimwith virtually two reversible leading edges.

Wheel Description and Optimum Camber Angle Defined

FIGS. 2-5 illustrate a general wheel assembly 100 for the bicycle 10 inFIG. 1 and cross-sectional views of a tubeless (FIG. 4) and clincher(FIG. 5) rims capable of being optimized by various embodiments hereindescribed below. Referring to FIGS. 2 and 3, a bicycle wheel 100 isdepicted showing a tire mounted thereto 110. The wheel 100 may include apair of planar-ring, parallel, and opposing brake surfaces, such assurface 111. Wheel 100 also includes convex curved carbon body sidewalls112 that make up part of the rim, a center hub 113, and a plurality ofspokes 114.

In FIG. 4, a cross section (taken from the line formed by theintersection 5-5 in FIG. 3) of wheel 100 is shown which is molded to bea one-piece wheel wherein the rim portion and body portion are made fromsimilar materials, in contrast to some two-piece wheels described below.The wheel of FIG. 4 has a tire mounting surface 121, a pair of straightand parallel braking surfaces 127, and a filled area of core material120. The body portion extends from the braking surfaces 127 and includessidewalls 119, and a hollow interior 126. The bulbous carbon bodyportion 134 typically includes a reinforced inner diameter portionhaving spoke attachment points which are typically apertures and whichmay include a metallic insert 125 for serving as an anchor for thespoke.

An acute angle 123 is formed between the braking surface 127 and theflexible sidewalls 119 and a line generally parallel to the axis of therim (see angle 123 and horizontal line drawn between the braking surface127 and the sidewall 119 of FIG. 4). Viewed another way, a radiallyextending line “E” that is disposed in the plane of the brakingsurface(s) 127 would intersect a radially extending line “F” that isdisposed tangentially to the sidewall(s) 119 of the body portion, at anaxially outwardly facing intersection angle “C”, which is referredherein as the camber angle. As described, for example, in U.S. Pat. No.5,975,645 to Sargent entitled “Carbon Bodied Bicycle Rim”, a typicalsuch camber angle has been less than 175° and preferably less than 165°.Example embodiments of the present invention, however, define the camberangle to be greater than 175°, but should be less than 178° (preferablybetween about 177.5° and 177.8°) for improved performance.

Note that the same or similar dimensional aspects apply to the clincherrim shown in FIG. 5 for defining the camber angle described above inFIG. 4. For example, shown in FIG. 4, a carbon body portion 134 includesa sidewall portions 119 extending from the radially outermost parts 139where the sidewalls 119 intersects with the braking surfaces 127, pastthe point of maximum width, and terminates at the radially innermostpoint 136, which is shown as being thicker than the sidewall 119, andthereby being reinforced. The axially extending, radially outwardlyfacing rim engaging surface 132, may include a circumferential crownportion and an interior 126 hollow portion to facilitate flex of thesidewalls.

Similar to FIG. 4, a camber angle “C” is defined by a radially extendingline “E” that is disposed in the plane of the braking surface 127intersects a radially extending line “F” that is disposed tangentiallyto the sidewall 119 of the body portion 150 at an axially outwardlyfacing intersection angle “C”. Again, camber angle “C” should be lessthan 178°, but greater than 175° (and preferably between 177.5° and177.8°) for improved performance as described in greater detail belowwith regard to FIG. 12. An acute angle 123 may be formed between a lineA perpendicular to the braking surface 138 and the first flexiblesidewall 152 (see angle 123 and line horizontal line drawn betweenbraking surface 127 and sidewall 119 of FIG. 5).

As will be described in greater detail below, the above camber angle maybe more accurately defined and represented using another exampleembodiment of tangency angles. More specifically, referring to FIG. 10B,leading edge (LE) and trailing edge (TE) tangency angles may be used asdescribed herein after for determining the optimum airfoil design(especially for a bi-directional or virtual dual LE airfoil).

Optimal Leading Edge and Max Width

As noted above, the Applicant realized an optimum leading edge width forpreventing a rim from stalling early in a crosswind, while maintainingstability without unnecessary drag. More specifically, it was determinedthat a rim with a leading edge width less than about 23 mm causes awheel to stall early in a crosswind, which greatly increases the drag atearlier yaw angles and exposes extremely adverse properties ofinstability and loss of control. Although a wider rim allows for betterstability in a crosswind, and most rims today include a leading edge ofgreater than 27 mm, beyond a certain point there becomes diminishingreturns based on an increase in drag from the wider rim itself. In otherwords, Applicant found that at widths beyond about 27 mm, the overalldrag (especially the rotating drag associated with a wider rim) increasedid not compensate for the later stall savings. In short, exampleembodiments provide for an optimal width of about 23 to 27 mm at theleading edge of a rim (more preferably between 24-26 mm), which preventsan early stall in crosswinds while still allowing suitable stabilitywithout unnecessary drag from other external forces acting on largerwidth wheels.

In short, increased width relative to the tire improves flow attachmenton the rim at the front of the wheel, and generally when significantlywider than the tire, flow attachment can be achieved. Nevertheless,there remains a limit on the front wheel of the bicycle due to thesystem drag (bicycle and wheel) becoming worse. Accordingly, exampleembodiments limit the width at the leading edge (and the max width)based on the desired shape at the trailing edge of the rim (i.e., thespoke hole face).

With the camber angle previously optimized at between about 175° and178°, and with the optimum width at the leading edge defined in the rageof 24 to 26 mm, the Applicant then determined a max width for theairfoil at an optimum location along the chord. Looking at FIGS. 6B and6D, it was found that the maximum width depth D where the maximum widthB should be optimally located at approximately 40% or less of the totalrim depth (as measured from the leading edge to the spoke face surface),and more specifically, at approximately 30% or less of the total rimdepth. More specifically, the Applicant found that wheels with largeconstants or gradually changing radius with a slightly wider section atapproximately 40% or less of the total rim depth allowed for significantincreases in yaw angles relative to the overall drag. For example, whenthe difference in width between the leading edge and the maximum width(which is located at chord percentage of less than 30%) is approximately0.75 mm, the overall surface separation of airflow along the sidewallsof the rim is dramatically reduced. This also allows higher yaw angleswithout stalling in crosswinds. In fact, as will be shown below withreference to FIG. 9, this and other embodiments described herein resultin a rim capable of achieving a very rare phenomenon known as negativedrag at specified yaw angles.

Referring to FIGS. 12A, 12B, and 12C, rim profiles for three differentrims (two 60 and one 35 mm) and styles are shown. In accordance withexample embodiments, generally speaking, the rim width preferablyremains between about 24 mm and 26 mm, and even more preferably at about25 mm. As also shown in the example rim profiles, a maximum width is setat a value less than 40% and more specifically less than 30% of theoverall depth. Note that these examples give specific measurements forthe various rim depths they represent; however, example embodiments arenot limited to such specific measurements. In fact, as describedthroughout the application, there are a myriad of shapes and combinationof rim sizes capable of taking advantage of the exemplary embodimentsdescribed herein. As such, any specific reference to dimensions of anyparticular size wheel and/or rim are used herein for illustrativepurposes only do not limit or otherwise narrow the scope of the presentinvention unless otherwise explicitly claimed.

Also note that in this example, there are two different profiles for the60 mm rim: one for the “front” rim and one for the “rear.” As notedabove, the front rim's airflow is based on the width of the leading edgeand the interaction of flow around the front fork. The rear wheel, onthe other hand, performs differently due to shielding from the frame andthe fact that width induces an even greater amount of drag on the frame.Accordingly, example embodiments provide for a rim set or systemconfigured to reduce the overall drag or optimize the overall airflow ofa bicycle by defining differing size and/or shape front and rear wheels.More specifically, example embodiments provide for a narrower rear wheelto reduce frame induced drag. Because of the partially shielded flowaround the rear wheel by the seat post, the airflow does not interactwith the tire in the same way that it does with the front. Therefore,the spoke face becomes the more dominant feature on the rear wheelssince airflow interacts more on the back edge of the rear rim than onits front. Thus, as described below, embodiments do not focus on theleading edge width or max width of the rear rim as much as the preferredwide radius spoke hole face for ensuring an rim airfoil ofbi-directional capabilities.

Similarly, other embodiments provide for a shallower front rim than therear since a deeper rim generates less drag, but due to side forceissues there becomes a limit to stability through the steering. In otherwords, example embodiments provide for the optimum rim set of a wider,shallower front rim and a deeper, narrower rear set up. Note, however,that the application also contemplates any sub combination of thedifferences and optimization. For example, as described below, theoverall shape of the rims may also differ; and thus, the use of thedifference in the rim sets based on the width and depth is used hereinfor illustrative purposes only and does not limit the claims unlessotherwise explicitly stated.

Spoke Face and Rim Shape

Other example embodiments described herein provide for fundamentalimprovements in performance and stability through a wheel or rim spokeface with a curvature radius as large as possible, but with a lowestpossible rate of change of curvature (i.e., continuous curvature). Thisunusual design feature differs significantly from prior art designs thatinclude sudden step changes in curvature rate along the spoke face. Morespecifically, as previously mentioned, airfoils generally take the formof a teardrop shape with the sidewalls converging into a relativelysharp point. In the case of wheel designs, however, such sharp pointneeded moderate flattening in order to accept spoke holes and for easein manufacturing. Nevertheless, generally an airfoil takes such form inorder to provide for good air attachment without high turbulence.

For example, FIGS. 6A and 6C illustrate a typical cross section andresulting airfoil shape, respectively, for typical rim designs. Asshown, a leading edge width “A” is defined generally by the distancebetween opposing braking surfaces 127. A max width “B” is also definedsome distance “D” along the chord length, which in prior art systems isusually greater than ⅓ of the overall rim depth. Based on these threemeasurements, a camber angle “C” is defined, which as described above isgenerally less than 175° in prior art systems, and preferably less than165°. Note that the trailing edge of the airflow or airfoil shapeairfoil in FIGS. 6A and 6C forms a narrowly tapered point, limited onlyby the diameter of the spoke and mechanism used to hold it in the rim.More specifically, conventional wisdom in the design of airfoil shapesfor wheels and rims attempt to mimic the traditional teardrop airfoildesign under the constraints or limitations of the necessary width ofthe spoke hole. As such, the rate of change of curvature at the spokehole face becomes extremely large at or near the holes or center of theface surface, but quickly diminishes thereafter. While such traditionalairfoil designs work well in stationary or unidirectional systems, suchdesigns are not optimized for airflow in the reverse direction. In otherwords, prior art airfoil design's only operate effectively in a singledirection, i.e., the front of the wheel; thus failing to achieve optimumairflow and resulting in unwanted air detachment and instability.

Example embodiments, however, have defined an optimum shape for airfoilthat operate in a bi-directional manner. More specifically, as shown inFIGS. 6B and 6D, a rim cross section and resulting airfoil shape areshown with a large radius spoke hole face operational as both a trailingand leading edge of an airfoil. In other words, when combined with thetire 110, the oval or disk like airflow pattern shown in FIG. 6D of therim provides virtually for two optimum leading edges that assist inmaintaining flow attachment in either the forward or reverse directionsof airflow travel. As seen, this notion of creating a large radius spokeface radius contradicts conventional wisdom in airfoil shapes,especially when evaluated in light of the unexpected stability and crosswind effects described below.

Note that although a particular shape of bi-directional rim is shown inFIG. 6B with the resulting airfoil in 6D, the actual shape and designwill vary depending on several factors as described herein. For example,the following table contains spreadsheet data showing various rimdesigns and considerations based on the specific rims' depth, width, andcamber angle relative to one another in accordance with exampleembodiments noted herein. Also note that the variables associated withthe overall design features may deviate from the optimum values anddesign; however, such deviations may still conform to the generalinventive concepts described herein. As such, any reference to aspecific shape rim or its dimensions are used herein for illustrativepurposes only, unless otherwise specifically claimed.

In accordance with one example embodiment, a process enables an optimumwheel by predefining a geometric shape based on a set of rim parametersand the above described bi-directional airfoil need. For example,referring to FIG. 6B, a combined geometry of rim 138 and tire 110 formsa leading edge LE diameter A and a trailing edge TE diameter B withconnecting sidewalls 119. Note that a further consideration may be thecamber angle C and/or the max width depth D at some percentage of thecord (as previously described and defined above). Alternatively, or inconjunction, the geometric shape and dimensions may be formed anddefined based on tangency angles (see FIG. 10B) for the LE or TE.Regardless of the exact parameters used or the number of definedvariables, the geometry formed by the intersection of the designparameters will resemble a geometry such as a parallelogram (e.g.,preferably a rectangle), ellipsis, or other similar form that sets theouter bounds of the airfoil shape needed at the spoke face 125.

Next, in order to maintain flow attachment at the spoke face where theairflow will loose the highest amount of energy, the spoke face radiusneeds to be maintained above a certain threshold limit. In addition, therate of change of curvature (i.e., the rate at which the curvaturechanges within on a per mm basis) needs to be evenly distributed alongthe spoke face 125. More specifically, the change of curvature from thetrailing edge of one sidewall 119 to the next 119 cannot exceed acertain threshold and, preferably, maintain a uniform distributionand/or change gradually or continuously across the entire spoke face125. In other words, if the geometric shape defines a square orrectangular boundary with a 90° turn at the max total depth where thespoke hole face begins (or ends), embodiments distribute the turning sothat the radius of curvature is as high as possible within that space.

In summary, example embodiments use two or more of airfoil parameters(e.g., LE width, max width, TE width, tire diameter, camber angle, maxdepth total, for defining a geometry (e.g., a rectangle with a givenwidth and depth) for a given rider application. With the outer limits ofthe airfoil shape set by the geometric shape, a virtual LE for thereverse flow is designed based on the objective of maintaining a highradius of curvature across the entire spoke face, while simultaneouslyholding the rate of change of curvature to a minimum. In other words,referring to FIG. 6D, based on the need for bi-directional airflow,example embodiments achieve an optimum airfoil design through setting ofat least two desired airfoil parameters, e.g., LE (A) and Max (B)diameters (preferably within the above described optimum solutions).These values then define geometric boundaries 130 used for then settinga curve 131 (i.e., spoke hole face 125) with a series of radial arcsabove a set threshold, the rate of which cannot change beyond a perlinear limit.

Note that such values of the smallest radius and highest rate of changeof curvature will again vary depending on the rim type, size, anddesired parameters. Nevertheless, preferably the radius or curvature(i.e., the minimum radius defined at any given point along the curve setby the bounds of the sidewall 119 and the max rim depth or edge of thespoke hole face 125) needs to be greater than about 6 mm (with anupper-lower bound generally not to exceed 15 mm, i.e., the smallestradius along the curvature no larger than 15 mm) to avoid flowseparation at the virtual leading edge (i.e., over the back of thewheel). Further, the gradual curvature transition (i.e., theincrease/decrease of curvature or radius to improve flow attachment)changes preferably by no more than about 60 mm/linear mm.

As shown in FIG. 9, one of the unexpected and advantageous features ofthe above described bi-directional airfoil is that the flow generates alow pressure region, which produces a lift or side force. This sideforce then results in lower drag in the direction of travel. Similarly,the balanced side force generated in each flow direction by thebi-directional airfoil shape does lessons the amount of steering torquefelt by the rider. In other words, with the balanced airflow designaround the rim, in the presence of a side wind the force remains equalon the front and rear part of the rim; therefore, the rider doesn't feelthe wind trying to turn the wheel.

As previously described, most bicycle rims that attempt to reduce dragwith standard airfoil shapes with large angles of discontinuity as thesidewalls approach the spoke hole or trailing edge of the airfoil-shapedrim and/or at the boundary line of the spoke holes themselves. Forexample, many competing rims have overly wide max widths at locationsfurther back along the chord, and therefore, they ultimately need tomake drastic adjustments in the slope of the sidewalls just after themax width location and often again at some distance close to the spokeholes. Further, most rims have large discontinuities in curvature at thespoke hole boundary (i.e., where the chord intersects the trailing edge)in order to approximate the typical airfoil sharper edge shape. Inaddition, this boundary line also inherently forms discontinuities dueto manufacturing techniques of some composite wheels designs (e.g., whencombining two halves or shells).

FIGS. 7, 10A, and 10B are graphical aids showing the differences in thechange of curvature between a previous rim design with largediscontinuities curvature (FIG. 7) and example embodiment rim designshaving continuous changes in curvature (FIGS. 10A and 10B). Thesefigures show a graphical aid tool commonly called a “curvature comb” or“hedgehog or porcupine curve.” The length of the lines (splines orspokes) running radially from the surface of the rim represent thecurvature (K). It should be noted that the length of these curvature (K)lines and the density of these lines are typically based on an arbitraryscale that best shows the curvature (K). The change of length betweeneach of these lines provide a visual aid for evaluating the change incurvature (∂K) as well as the rate of change (or acceleration) in thechange of curvature (∂K′) along the length of the rim.

Continuity between surfaces (i.e., how smoothly they connect to oneanother) can be characterized based on a number different levels orclasses of continuity. Positional or touching continuity, commonlyreferred to as G0 continuity, occurs whenever the end positions of twocurves or surfaces touch. With G0 continuity, the curves or surfaces canmeet at an angle, thereby having sharp corners or edges. Tangential orG1 continuity requires the end vectors of the curves or surfaces to beparallel where they meet, thereby ruling out sharp edges. With G1continuity, the curves or surfaces share a common tangent direction atthe location where two curves or surfaces meet. To put it another way,G1 continuity means that the two curves not only touch, but they go thesame direction at the point where they touch G2 or curvature continuityfurther requires the end vectors to be of the same length and rate oflength change. In other words, G2 continuity additionally requires thatthe curves (or surfaces) not only go the same direction when they meet,but also have the same radius (R) or curvature (K) that point where theymeet. G3 or curvature acceleration continuity requires an even a higherdegree of continuity than G2 by adding another requirement to thecontinuity, planar acceleration. Curves that are G3 continuous touch(G0), go the same direction (G1), have the same radius or curvature(G2), and that radius (R) or curvature (K) is accelerating at the samerate where the curves or surfaces meet.

FIG. 7 illustrates one example of a previous rim design having largediscontinuities in curvature. As can be seen, the rim has a number ofareas where there are dramatic changes or discontinuities in the rate ofchange of curvature. The FIG. 7 rim can be characterized as having atmost G1 or tangential continuity. Such discontinuous curvatures (e.g.,the one shown in FIG. 7) or poorly designed airfoil rims (and especiallythose with discontinuities in the rate of change of curvature around thespoke hole face) create unwanted drag for less than optimal performance.In other words, due to conventional wisdom about airfoils and currentmanufacturing limitations, typical so called “high performance” wheelsstall prematurely in crosswinds and produce unwanted airflow surfacedetachment and turbulence.

In contrast, the rims depicted in FIGS. 10A and 10B exhibit G3continuity. As shown in FIGS. 10A and 10B, the example embodimentsprovide for an evenly distributed rate of change of curvature over theentire surface of the rim and a continuous or gradual rate of change ofcurvature (also known as a class “A” surface modeling) along the spokeface or boundary. More specifically, the rate of change of curvature isuniformly distributed or gradually occurs over the entire geometriclength of the spoke face, which varies in length between about 51 and 60mm depending on the rim depth (see the chart below for more details onhow such geometries vary). The radius of curvature is ever reducing fromthe sidewall to the center of the spoke face. In particular, the radiusis always reducing around the spoke face from a maximum at theintersection with the sidewall to a minimum at the center of the spokeface. In other words, example embodiments limit the linear turningradius of a spoke face from the sidewall to the spoke hole face itselfin order to ensure airflow attachment, especially in the reverse airflowdirection (i.e., on the back side of the rim). Related to such change isthe actual radius size across the spoke hole face (see, e.g., FIG. 8),wherein other embodiments (as previously mentioned) attempt to keep theradius at any given point above a threshold (e.g., above 6 mm with alower limit of not greater than about 15 mm).

The family of curves in FIG. 11 show how the rate of change in thechange in curvature (i.e., second derivative of curvature or ∂K′) isgradual throughout the entire sidewall and spoke face. Again, it shouldbe recognized that the rims in FIG. 11 have G3 continuity. Moreover, therims in the illustrated examples start with a high radius of curvatureat the sidewall (greater than 100 mm) and finish with a small radius ofcurvature (approximately 10 mm) at the spoke face. As can be seen inFIG. 11, the derivative in the change of curvature (∂K′) has beenminimized as much as the geometry will allow.

Although no upper radius need be set, in some instances the maximumradius size is bound by the geometric limitations of the rim size andshape itself. For example, as shown in FIG. 12C and the table below, ashallow 35 mm rim does not allow enough length to achieve a large radiusof curvature, so the max radius is only 150 mm. On a deep section rim(e.g., the 70 and 85 shown in the table below), however, much largercurvatures (e.g., 420 mm and above) are possible. Note that the sidewall119 shape is compromised so that it bends into the spoke face. As such,considering the sidewall when flow comes from the tire (i.e., theforward direction), the leading edge angle

It should be noted that this unconventional design for a spoke facesurface advantageously and surprisingly generates side forces at higheryaw angles so that the part of the wheel behind a fork turns the wheelback into the wind. As such, example embodiments that optimizing theside force (lift) on the front part of the rim ahead of the fork and theefficiencies gained from the spoke hole face in the rear part of therim, the wheel remains stable in windy conditions.

Referring again to FIG. 7, as well as the corresponding data shown inTables 1 and 2 below, a typical cross section of a rim withdiscontinuity across the entire surface of the rim, and especially atthe spoke face and leading edge. It should be noted that for all of thetables below that the radius (R) and its inverse, curvature (K) valuesare given at individual points. While the gradient or rate of change ofcurvature (∂K) has been provided in the tables below, it should beappreciated these changes could also be represented by the rate ofchange in the radius of curvature per traveling distance (∂R). Note thatalthough the rate of change of radius is steady over various areas ofthe rim surface, such holding the radius steady creates the steppingpattern noted from the transitions. As previously mentioned, this istypically due to such things as: high camber angle levels at thesidewalls; the maximum width occurring too far down the distance of thechord; and/or the spoke face occurring over a short distance, whichoccurs from their failure to use high radius of curvatures overall (asthe present invention does). In other words, without the advantageousrecognition of the present invention for optimizing the overallaerodynamic properties of a rim, the prior art designs, like the oneshown in FIG. 7, result in high curvature rates (i.e., typically largerthan 60 mm/linear mm. As such, the prior art fails to achieve an optimumbi-directional airfoil rim.

Table 1 illustrates the various dimensions of the rim shown in FIG. 7.

TABLE 1 Measurement Data for a Prior Art Rim of FIG. 7 Prior Art RimLeading Edge (x) −5.92 Leading Edge Width 16.927 LE Side Wall (x) −3.03LE Side Wall Width 24.018 LE Tangency Angle TE Tangency Angle Max Width(x) 16.6641 Max Width 27.26 Max Width Chord Spoke Face (X) 55.2808 MaxDepth Total (mm) 61.2008 Camber Angle (Sidewall) 4.7117 Max Width (%Chord) 36.9016418 Sidewall LE Radius 101.6 Sidewall TE Radius 141.522Sidewall Length 38.82112 Gradient (RadCurv/Linear mm) 1.02835776 TotalLength of spoke face 45.28 Maximum radius of curvature gradient 13.67

Table 2 shows the radius of curvature and gradient measurements alongwith the gradient change at various sample locations along the spokeface of the prior art rim depicted in FIG. 7. Looking again at FIG. 7(as well as shown in Table 2 below), the changes in curvature are verymuch discontinuous. As will be described in greater detail below, therate of change in the change of curvature/gradient (∂K′) or the seconddifferential of the curvature (K) for the prior art rim in FIG. 7 is amagnitude of ten times larger than the inventive rim designs describedherein.

TABLE 2 Rate of Change of Curvature Data of Prior Art Rim of FIG. 7Curvilinear Gradient Position Curvilinear Gradient Derivative AlongSpoke Radius Curvature Distance (∂K) (∂K′) Sample Face (mm) (mm) (K) (L)(mm) (mm/mm) (mm/mm²) 0 0 31.75 0.031 1 1.617 31.75 0.031 1.617 0.000 23.234 31.75 0.031 1.617 0.000 3 4.851 31.75 0.031 1.617 0.000 0 4 6.46831.75 0.031 1.617 0.000 0 5 8.085 31.75 0.031 1.617 0.000 0 6 9.70231.75 0.031 1.617 0.000 0 7 11.319 31.75 0.031 1.617 0.000 0 8 12.9369.648 0.104 1.617 0.045 0.0276 9 14.553 9.648 0.104 1.617 0.000 0.027610 16.17 9.648 0.104 1.617 0.000 0 11 17.787 9.648 0.104 1.617 0.000 012 19.404 9.648 0.104 1.617 0.000 0 13 21.021 9.648 0.104 1.617 0.000 014 22.638 9.648 0.104 1.617 0.000 0 Maximum 0.045 0.0276

The following tables illustrate some measured values of variousprototype rims constructed in accordance with exemplary embodimentsdescribed herein. Although embodiments may reference values therein,such reference is for illustrative purposes and does not limit orotherwise narrow the scope of the present invention unless otherwiseexplicitly claimed.

Table 3 below lists the various dimensions of the 35, 45, 60, 70, 85,and 95 millimeter rims respectively illustrated in FIGS. 13, 14, 15, 16,17, and 18. All of the measurements in the tables below are inmillimeters unless specified otherwise, such as specifying a specificpercentage. Table 3 below illustrates the various dimensions of thevarious size rims according to various examples. For each size rim, theradius of curvature was measured at various positions along the spokeface. The following tables will describe those measurements as well asthe gradient and change in gradient at the specific points. It should benoted that the camber angle measurements in Table 3 as well as elsewherein the present application are measured from the leading edge ratherthan some other location, such as from behind the braking surface.

TABLE 3 Various Dimensions of Rims Illustrated in FIGS. 13, 14, 15, 16,17, and 18 35 mm 45 mm 60 mm 70 mm 85 mm 95 mm Leading Edge (x) −6.49−6.02 −6.49 −6.02 −6.49 −6.49 Leading Edge Width 23.34 22.26 23.24 22.2723.34 22.27 LE Side Wall (x) −5.29 −5.29 −6.49 −5.29 −6.49 −5.29 LE SideWall Width 24.95 22.95 24.95 22.95 24.95 22.95 LE Tangency Angle 4.864.86 4.88 4.86 4.88 4.88 TE Tangency Angle 3.72 4.22 4.57 5.08 6.08 5.08Max Width (x) 0.82 6.34 10.40 17.27 17.05 31.53 Max Width 25.44 23.9926.28 24.68 26.89 25.62 Max Width Chord Spoke Face (X) 28.28 38.51 53.0263.49 78.40 88.50 Max Depth Total 34.77 44.53 59.51 69.51 84.89 94.99(mm) Camber Angle 2.30 2.45 2.42 2.21 2.49 2.10 (Sidewall) Max Width21.04 27.76 28.37 33.50 27.73 40.03 (% Chord) Sidewall LE Radius 58.80145.80 182.20 233.00 257.23 368.00 Sidewall TE Radius 136.30 164.80205.38 327.14 421.04 443.00 Sidewall Length 13.60 23.60 33.44 41.8661.00 69.70 Gradient 5.70 0.81 0.69 2.25 2.69 6.36 (RadCurv/Linear mm)START Radius/ 4.32 6.18 5.45 5.57 4.22 5.28 Length Radius Ratio ENDRadius/Length 10.02 6.98 6.14 7.82 6.90 6.36 Radius Ratio Spoke FaceStart 136.30 164.80 205.38 327.14 421.04 443.00 Radius Spoke Face Min10.30 8.37 6.89 7.02 6.45 6.12 Radius Total Length of Spoke 57.48 51.4660.32 53.21 55.25 57.20 Face Maximum Radius of 18.12 23.05 24.16 61.2983.54 81.82 Curvature Gradient

To help illustrate where the measurements occur in Tables 2 and 4-9,FIG. 19 illustrates a cross-sectional view of a rim 140 and the variouslocation measurements along the spoke face. Reference numeral 142 inFIG. 19 indicates the initial or zero sample location reference point,and reference numeral 144 indicates the stop or end point for the samplemeasurements. For the measurements in Table 2, fifteen (including samplepoint zero) measurements of radius of curvature were made from theinitial sample location 142 (P₀) to the end point 144 (P₁₄), and inTables 3-9, thirteen samples were measured (i.e., sample points P₀ toP₁₂) between the initial sample location 142 to the end point 144. Itshould be noted that since the rim 140 is symmetrical, the radius ofcurvature (K) should generally be the similar at similar sides of thespoke face. The curvilinear position along the spoke face was measuredrelative to the initial sample location 142. For example, samplelocation number 1 in Table 4 was 2.4 mm from the sample point 0 on thespoke face. At each of the sample points, the radius was measured. Itshould be appreciated that the rate of change of curvature or gradient(∂K), which is indicated by column header “Gradient” in Tables 2 and4-9, is calculated using Equation 2. The derivative of the gradient(∂K′), which has the “Gradient Derivative” column heading, shows thesecond derivative of the curvature (K) per curvilinear travel distance(L). In other words, the derivative of the gradient column representsthe rate of rate of change in the change of curvature, or in otherwords, the acceleration of the curvature. It should be noted that thegradient derivative (∂K′) column in the tables has been calculated usingthe absolute value of the difference between the gradients. These tablesalso provide the maximum gradient and the maximum change in gradient.

Table 4 below provides the rate of change of curvature (or gradient)data for the 45 mm rim illustrated in FIG. 14 and referenced in Table 3.

TABLE 4 Rate of Change of Curvature Data for 35 mm Rim Illustrated inFIG. 13 Curvilinear Gradient Position Curvilinear Gradient DerivativeAlong Spoke Radius Curvature Distance (∂K) (∂K′) Sample Face (mm) (mm)(K) (L) (mm) (mm/mm) (mm/mm²) 0 0 136.30 0.0073 1 2.395 103.30 0.00972.40 0.0010 2 4.79 59.90 0.0167 2.40 0.0029 0.0008 3 7.185 37.50 0.02672.40 0.0042 0.0005 4 9.58 26.00 0.0385 2.40 0.0049 0.0003 5 11.975 19.500.0513 2.40 0.0054 0.0002 6 14.37 15.40 0.0649 2.40 0.0057 0.0001 716.765 12.90 0.0775 2.40 0.0053 0.0002 8 19.16 11.40 0.0877 2.40 0.00430.0004 9 21.555 10.70 0.0935 2.40 0.0024 0.0008 10 23.95 10.40 0.09622.40 0.0011 0.0005 11 26.345 10.30 0.0971 2.40 0.0004 0.0003 12 28.7410.30 0.0971 2.40 0.0000 0.0002 Maximum 0.0057 0.0008

Table 5 below provides the rate of change of curvature (or gradient)data for the 45 mm rim illustrated in FIG. 14 and referenced in Table 3.

TABLE 5 Rate of Change of Curvature Data for 45 mm Rim Illustrated inFIG. 14 Curvilinear Gradient Position Curvilinear Gradient DerivativeAlong Spoke Radius Curvature Distance (∂K) (∂K′) Sample Face (mm) (mm)(K) (L) (mm) (mm/mm) (mm/mm²) 0 0.00 165.90 0.0060 1 2.14 118.83 0.00842.14 0.0011 2 4.29 91.76 0.0109 2.14 0.0012 0.0000 3 6.43 42.34 0.02362.14 0.0059 0.0022 4 8.58 29.25 0.0342 2.14 0.0049 0.0005 5 10.72 21.490.0465 2.14 0.0058 0.0004 6 12.86 16.57 0.0604 2.14 0.0064 0.0003 715.01 13.54 0.0739 2.14 0.0063 0.0001 8 17.15 11.36 0.0880 2.14 0.00660.0001 9 19.30 9.82 0.1018 2.14 0.0064 0.0001 10 21.44 9.01 0.1110 2.140.0043 0.0010 11 23.58 8.54 0.1171 2.14 0.0029 0.0007 12 25.73 8.370.1195 2.14 0.0011 0.0008 Maximum 0.0066 0.0022

Table 6 below provides the rate of change of curvature (or gradient)data for the 60 mm rim illustrated in FIG. 15 and referenced in Table 3.

TABLE 6 Rate of Change of Curvature Data for 60 mm Rim Illustrated inFIG. 15 Curvilinear Gradient Position Curvilinear Gradient DerivativeAlong Spoke Radius Curvature Distance (∂K) (∂K′) Sample Face (mm) (mm)(K) (L) (mm) (mm/mm) (mm/mm²) 0 0.00 205.45 0.0049 1 2.51 158.62 0.00632.51 0.0006 2 5.02 97.99 0.0102 2.51 0.0016 0.0004 3 7.53 64.64 0.01552.51 0.0021 0.0002 4 10.04 44.89 0.0223 2.51 0.0027 0.0002 5 12.55 32.660.0306 2.51 0.0033 0.0002 6 15.06 24.21 0.0413 2.51 0.0043 0.0004 717.57 18.35 0.0545 2.51 0.0053 0.0004 8 20.08 13.91 0.0719 2.51 0.00690.0007 9 22.59 10.79 0.0927 2.51 0.0083 0.0005 10 25.10 8.73 0.1145 2.510.0087 0.0002 11 27.61 7.43 0.1346 2.51 0.0080 0.0003 12 30.11 6.890.1452 2.51 0.0042 0.0015 Maximum 0.0087 0.0015

Table 7 below provides the rate of change of curvature (or gradient)data for the 70 mm rim illustrated in FIG. 16 and referenced in Table 3.

TABLE 7 Rate of Change of Curvature for 70 mm Rim Illustrated in FIG. 16Curvilinear Gradient Position Curvilinear Gradient Derivative AlongSpoke Radius Curvature Distance (∂K) (∂K′) Sample Face (mm) (mm) (K) (L)(mm) (mm/mm) (mm/mm²) 0 0.00 327.31 0.0031 1 2.22 191.42 0.0052 2.220.0010 2 4.43 93.92 0.0106 2.22 0.0024 0.0007 3 6.65 54.57 0.0183 2.220.0035 0.0005 4 8.87 36.66 0.0273 2.22 0.0040 0.0003 5 11.09 26.130.0383 2.22 0.0050 0.0004 6 13.30 19.46 0.0514 2.22 0.0059 0.0004 715.52 14.89 0.0672 2.22 0.0071 0.0005 8 17.74 11.76 0.0851 2.22 0.00810.0004 9 19.95 9.65 0.1036 2.22 0.0084 0.0001 10 22.17 8.19 0.1221 2.220.0083 0.0000 11 24.39 7.40 0.1352 2.22 0.0059 0.0011 12 26.60 7.020.1426 2.22 0.0033 0.0012 Maximum 0.0084 0.0012

Table 8 below provides the rate of change of curvature (or gradient)data for the 85 mm rim illustrated in FIG. 17 and referenced in Table 3.

TABLE 8 Rate of Change of Curvature Data for 85 mm Rim Illustrated inFIG. 17 Curvilinear Gradient Position Curvilinear Gradient DerivativeAlong Spoke Radius Curvature Distance (∂K) (∂K′) Sample Face (mm) (mm)(K) (L) (mm) (mm/mm) (mm/mm²) 0 0.00 420.25 0.0024 1 2.30 227.95 0.00442.30 0.0009 2 4.60 108.96 0.0092 2.30 0.0021 0.0005 3 6.91 61.39 0.01632.30 0.0031 0.0004 4 9.21 42.89 0.0233 2.30 0.0031 0.0000 5 11.51 29.100.0344 2.30 0.0048 0.0008 6 13.81 21.36 0.0468 2.30 0.0054 0.0003 716.11 16.52 0.0605 2.30 0.0060 0.0002 8 18.42 13.04 0.0767 2.30 0.00700.0005 9 20.72 10.08 0.0992 2.30 0.0098 0.0012 10 23.02 7.99 0.1251 2.300.0113 0.0007 11 25.32 6.95 0.1440 2.30 0.0082 0.0013 12 27.62 6.450.1551 2.30 0.0048 0.0015 Maximum 0.0113 0.0015

Table 9 below provides the rate of change of curvature (or gradient)data for the 95 mm rim illustrated in FIG. 18 and referenced in Table 3.

TABLE 9 Rate of Change of Curvature Data for 95 mm Rim Illustrated inFIG. 18 Curvilinear Gradient Position Curvilinear Gradient DerivativeAlong Spoke Radius Curvature Distance (∂K) (∂K′) Sample Face (mm) (mm)(K) (L) (mm) (mm/mm) (mm/mm²) 0 0.00 443.00 0.0023 1 2.38 248.00 0.00402.38 0.0007 2 4.77 101.30 0.0099 2.38 0.0025 0.0007 3 7.15 68.03 0.01472.38 0.0020 0.0002 4 9.53 45.47 0.0220 2.38 0.0031 0.0004 5 11.92 31.430.0318 2.38 0.0041 0.0004 6 14.30 23.02 0.0434 2.38 0.0049 0.0003 716.68 16.62 0.0602 2.38 0.0070 0.0009 8 19.07 12.45 0.0803 2.38 0.00850.0006 9 21.45 9.73 0.1028 2.38 0.0094 0.0004 10 23.83 7.61 0.1314 2.380.0120 0.0011 11 26.22 6.41 0.1559 2.38 0.0103 0.0007 12 28.60 6.120.1635 2.38 0.0032 0.0030 Maximum 0.0120 0.0030

As mentioned before, the rims designed according to the presentinvention have a rate of change of curvature or gradient (∂K) that isgradual and continuous. Specifically, the rims along the sidewalls andspoke face have G3 continuity. To quantify these properties, the rimsaccording to the present invention do not have dramatic changes incurvature such that rate of change of curvature or gradient (∂K) is low(i.e., gradual) and the acceleration of the curvature (i.e., the rate ofchange in the rate of change of curvature) or gradient derivative (∂K′)is also low (i.e., continuous). Out of all of the example embodimentsabove, the maximum gradient was 0.0113 mm/mm for the 80 mm rim, and themaximum gradient derivative (∂K′) was 0.0030 mm/mm² for the 95 mm rim.These values are in sharp contrast to the prior art rim in FIG. 7 thathas an abrupt and discontinuous rate of change of curvature.Specifically, the prior art rim in FIG. 7 has a maximum rate of changeof curvature (∂K) of 0.045 mm/mm and a maximum rate of change in therate of change of curvature (∂K′) of 0.0276 mm/mm². These values for theFIG. 7 rim are orders of magnitude larger than the maximum values inTables 3-9. As can be seen, the maximum rate of change of curvature (∂K)for the FIG. 7 rim is at least almost four (4) times larger than therims of Tables 3-9 and the maximum gradient derivative (∂K′) is at leastalmost ten (10) times larger than the rims of Tables 3-9. To put itanother way, the rims according to the present invention have a maximumrate of change of curvature (∂K) of less than 0.045 mm/mm, and morepreferably about at most 0.020 mm/mm and still more preferably about atmost 0.0120 mm/mm, and still yet more preferably about at most 0.0113mm/mm. Alternatively or additionally, the rims according to the presentinvention have a maximum rate of change in the rate of change ofcurvature or gradient derivative (∂K′) less than 0.0276 mm/mm², and morepreferably, about at most 0.0100 mm/mm², and still more preferably aboutat most 0.004 mm/mm², and still yet more preferably about at most 0.0030mm/mm².

Moreover, it is contemplated that these maximum values can differdepending on the size of the rim (see, Tables 3-9). For example, a 35 mmrim according to the present invention has a maximum rate of change ofcurvature (∂K) of about at most 0.0057 mm/mm and a maximum rate ofchange in the rate of change of curvature or gradient derivative (∂K′)of about no more than 0.0008 mm/mm². A 45 mm rim according to thepresent invention has a maximum rate of change of curvature (∂K) ofabout at most 0.0066 mm/mm and a maximum rate of change in the rate ofchange of curvature or gradient derivative (∂K′) of about at most 0.0022mm/mm². A 60 mm rim according to the present invention has a maximumrate of change of curvature (∂K) of about at most 0.0087 mm/mm and amaximum rate of change in the rate of change of curvature or gradientderivative (∂K′) of about at most 0.0015 mm/mm². A 70 mm rim accordingto the present invention has a maximum rate of change of curvature (∂K)of about at most 0.0084 mm/mm and a maximum rate of change in the rateof change of curvature or gradient derivative (∂K′) of about at most0.0012 mm/mm². An 85 mm rim according to the present invention has amaximum rate of change of curvature (∂K) of about at most 0.0113 mm/mmand a maximum rate of change in the rate of change of curvature orgradient derivative (∂K′) of about at most 0.0015 mm/mm². A 90 mm rimaccording to the present invention has a maximum rate of change ofcurvature (∂K) of about at most 0.0120 mm/mm and a maximum rate ofchange in the rate of change of curvature or gradient derivative (∂K′)of about at most 0.0030 mm/mm².

The above tables assist in describing another example embodiment, forexample those results shown in FIG. 9. As shown, the turbulent boundarylayer created by the optimum properties defined above for the presentinvention remains adhered to the surface of the wheel better than in theprior art wheels and keeps the boundary layer from separating from theair engaging side surfaces longer than the more laminar boundary layerof the air that occurs with the prior art, surface feature wheels. Thisalso results in less interference drag between the air flowing past thewheel and the bicycle frame members such as the seat stays, chain stays,and the front wheel for blades.

This reduction in drag allows the wheel to slip through the air withless resistance, which enables the rider to either ride more quicklywith the same amount of effort, or alternately to ride at the same speedwith less effort, when compared to riding a bicycle with the prior artwheels. Furthermore, the resultant wheels provide for a quiet, stable,smoother, faster and crosswind balanced ride over the prior art rims.

The graph in FIG. 9 shows the actual results obtained in wind tunneltests for wheels of the present invention versus several different priorart types of wheels. As shown, the wheel of the present inventioncreates a lower drag force than any of the other wheel types across mostof the range of the graph, particularly between angles of 10 to 12degrees. This can be attributed to lower surface friction of thewindward side and better adhesion of the airflow to the leeward side ofthe wheel due to the continual rate of change of curvature and otheroptimizations noted above.

For example, FIGS. 12A, 12B, and 12C illustrate three different profileviews with dimensions as described herein. In one embodiment showntherein, the front wheel has a larger leading edge width than the rearwheel. Applicant found that because the rear wheel sits behind the frameseat tube, a wider rim does not necessarily help flow attachment inhigher crosswinds. In fact, the wider rim has a bigger adverse effect onframe drag than the front primarily due to the fact there areeffectively two forks (seat stay and chain stay). In contrast, smallerwidth rims (e.g., about 24 mm widths) perform terribly when mounted onthe front of the bicycle, but wider rims do perform better compared tothose mounted in the rear. As such, embodiments described herein furtheroptimize airflow around the entire bicycle structure by providing wheelsets with wider front wheel and narrower rear wheel assemblies.

Also shown in FIG. 12C, a shallow 35 mm rim does not allow enough lengthto achieve a large radius of curvature, so the max radius is only 150mm.

The present invention may be embodied in other specific forms withoutdeparting from its spirit or essential characteristics. The describedembodiments are to be considered in all respects only as illustrativeand not restrictive. The scope of the invention is, therefore, indicatedby the appended claims rather than by the foregoing description. Allchanges which come within the meaning and range of equivalency of theclaims are to be embraced within their scope.

1. An apparatus, comprising: a bicycle rim having a spoke face, aleading edge at an outer radial edge of the bicycle rim, a sidewallextending from the spoke face to the leading edge, and wherein thesidewall has a maximum rate of change in the rate of change of curvatureless than 0.0276 mm/mm².
 2. The apparatus of claim 1, wherein thesidewall has a maximum rate of change of curvature less than 0.045mm/mm.
 3. The apparatus of claim 1, wherein a radius at any point alongthe spoke face is above 6 mm and the rate of change of curvature alongthe spoke face is less than 85 mm per linear mm.
 4. The apparatus ofclaim 1, wherein a radius at any point along the spoke face has a lowerlimit not greater than 15 mm.
 5. The apparatus of claim 1, wherein thespoke face has a length between 51 mm and 60 mm.
 6. The apparatus ofclaim 1, wherein the bicycle rim has a radius of curvature of less thanor equal to 420 mm along the spoke face and the sidewall.
 7. Theapparatus of claim 1, wherein the bicycle rim at the leading edge has awidth of 23 mm to 27 mm.
 8. The apparatus of claim 1, wherein thebicycle rim has a maximum width located at approximately 40% or less ofthe overall rim depth as measured from the leading edge.
 9. Theapparatus of claim 8, wherein the maximum width is approximately 0.75 mmwider than the width of the bicycle rim at the leading edge.
 10. Theapparatus of claim 1, wherein all of the sidewall is curved.
 11. Theapparatus of claim 1, wherein the sidewall has a maximum radius ofcurvature that is at most 443 mm.
 12. The apparatus of claim 1, whereinall adjoining curves along the sidewall from the spoke face to theleading edge have: positional continuity (G0) where the curves touch;tangential continuity (G1) in which the curves to share a common tangentdirection where the curves touch; curvature continuity (G2) in which thecurves to share a common curvature where the curves touch; and curvatureacceleration continuity (G3) in which the common curvature acceleratesat a common rate where the curves touch.
 13. The apparatus of claim 1,further comprising: a bicycle wheel including the bicycle rim, a hub,and one or more spokes extending from the spoke face, wherein the spokesconnect the bicycle rim to the hub.
 14. The apparatus of claim 1,wherein the radius of curvature reduces from the sidewall to the centerof the spoke face.
 15. An apparatus, comprising: a bicycle rim having aninner radial periphery, an outer radial periphery, a surface extendingfrom the inner radial periphery to the outer radial periphery, andwherein all adjacent curves along the surface have curvatureacceleration continuity (G3) in which the curvature where the curvestouch accelerates at a common rate.
 16. The apparatus of claim 15,wherein all of the curves along the surface have: positional continuity(G0) where the curves touch; tangential continuity (G1) in which thecurves to share a common tangent direction where the curves touch; andcurvature continuity (G2) in which the curves to share a commoncurvature where the curves touch.
 17. The apparatus of claim 15,wherein: the inner radial periphery includes a spoke face from where oneor more spokes extend; the outer radial periphery includes a leadingedge where a tire engages the bicycle rim; and the surface includes asidewall that extends from the spoke face to the leading edge.
 18. Theapparatus of claim 17, further comprising: a bicycle wheel including thebicycle rim, a hub, and the spokes extending from the spoke face,wherein the spokes connect the bicycle rim to the hub.
 19. The apparatusof claim 15, wherein the surface has: a maximum rate of change ofcurvature less than 0.045 mm/mm; and a maximum rate of change in therate of change of curvature less than 0.0276 mm/mm².
 20. The apparatusof claim 15, wherein the surface has a maximum radius of curvature thatis at most 443 mm.
 21. The apparatus of claim 15, wherein the surfacelacks a flat section.
 22. The apparatus of claim 15, wherein the surfacehas a maximum rate of change of curvature of less than 0.045 mm/mm. 23.The apparatus of claim 15, wherein the surface has a maximum rate ofchange of curvature of at most 0.020 mm/mm.
 24. The apparatus of claim15, wherein the surface has a maximum rate of change of curvature of atmost 0.0120 mm/mm.
 25. The apparatus of claim 15, wherein the surfacehas a maximum rate of change of curvature of at most 0.0113 mm/mm. 26.The apparatus of claim 15, wherein the surface has a maximum rate ofchange in the rate of change of curvature of at most 0.0276 mm/mm². 27.The apparatus of claim 15, wherein the surface has a maximum rate ofchange in the rate of change of curvature of at most 0.0100 mm/mm². 28.The apparatus of claim 15, wherein the surface has a maximum rate ofchange in the rate of change of curvature of at most 0.0040 mm/mm². 29.The apparatus of claim 15, wherein the surface has a maximum rate ofchange in the rate of change of curvature of at most 0.0030 mm/mm². 30.The apparatus of claim 15, wherein the surface has a maximum rate ofchange of curvature of at most 0.0057 mm/mm and a maximum rate of changein the rate of change of curvature of no more than 0.0008 mm/mm². 31.The apparatus of claim 15, wherein the surface has a maximum rate ofchange of curvature of at most 0.0066 mm/mm and a maximum rate of changein the rate of change of curvature of at most 0.0022 mm/mm².
 32. Theapparatus of claim 15, wherein the surface has a maximum rate of changeof curvature of at most 0.0087 mm/mm and a maximum rate of change in therate of change of curvature of at most 0.0015 mm/mm².
 33. The apparatusof claim 15, wherein the surface has a maximum rate of change ofcurvature of at most 0.0084 mm/mm and a maximum rate of change in therate of change of curvature of at most 0.0012 mm/mm².
 34. The apparatusof claim 15, wherein the surface has a maximum rate of change ofcurvature of at most 0.0113 mm/mm and a maximum rate of change in therate of change of curvature of at most 0.0015 mm/mm².
 35. The apparatusof claim 15, wherein the surface has a maximum rate of change ofcurvature of at most 0.0120 mm/mm and a maximum rate of change in therate of change of curvature of at most 0.0030 mm/mm².